Prior art processes for making fuming nitric acid involve steps that are energy intensive and thereby increase the cost of carrying out the processes. A conventional process generally involves treating oxides of nitrogen in the presence of oxygen and water to form nitric acid, and then concentrating the aqueous nitric acid using one or more distillation steps to remove the water. An example of such a process is shown in U.S. Pat. No. 1,989,267 to Care et al. Another conventional process first produces 63% nitric acid which is then mixed with concentrated sulfuric acid. Fuming nitric acid is then recovered from this mixture by distillation at temperatures ranging from 150.degree. to 200.degree. C., leaving as a co-product spent sulfuric acid containing the removed water which must then be either reconcentrated or disposed of. These processes involve considerable energy expenditure to achieve the distillation, and involve substantial waste acid disposal problems.
The purpose of this invention is to eliminate the above mentioned disadvantages by providing an improved process involving no distillation, and in which there is no need to add concentrated sulfuric acid to intermediately formed hydrous nitric acid for water removal purposes.